Flat Car Friday - the same prototype?

Green River, Wyoming, Keith Ardinger photo

I have this Spokane International flat car on my list of projects, likely to appear in kit form (car nos. 5001-5075, built 1951 by American Car & Foundry.) I am hopeful that the Museum of Transportation in St. Louis has drawings and am awaiting their reply to my query. In the meantime, I have been examining my collection of flat car photos for fodder for this blog. I came across the photo shown below and was struck by the similarities to the SI flat shown above (below from St. Louis - San Francisco car nos. 95800-95899, built 1951 by American Car & Foundry.) Dimensionally, the cars are identical and the overall look plus the arrangement of details, notably the type and spacing of the stake pockets, leads me to believe that they were from the same design. I have also inquired about drawings of these Frisco cars to compare, should both be available. I am keeping a keen eye out to see if ACF built other flats like these at around the same time. More about the load on the SI flat coming in the following days, too.

P.S. The SP's F-50-16 class, while similar at first blush and built by ACF, is not the same design as the cars illustrated herein.

Fayetteville, North Carolina, Dec. 23, 1951, Col. Chet McCoid photo, Bob's Photo